Rice±wheat rotations, practised in 12.5 million ha in Indo-Gangetic Plain region (IGPR), are the most important production
system for food security of south Asian countries. Recent reports, however, indicate that the system is under production fatigue
as yields have started declining due to continuous rice±wheat cultivation. We analysed the yield trends and effect of fertiliser
NPK application, alone or in combination with farmyard manure (FYM), green manure (GM) or wheat crop residue (CR)
incorporation, on the changes in soil organic carbon (OC) and available NPK contents. Data of a long-term experiment
conducted at six locations in the IGPR and at one location in the Central Highlands and Plateau region of India, adjacent to
IGPR, revealed that yields of rice and wheat were constantly greater in all the years when complete doses of NPK were
applied through fertilisers, or 50% dose of NPK were applied through fertilisers along with organic materials compared to that
in unfertilised-control. At Ludhiana and Pantnagar, where yield levels during initial years of the experiment were relatively
high, a declining trend in yield was observed over years in all the treatments. At other locations, rice or wheat yield trends in
the treatments receiving complete doses of fertiliser NPK were generally not signi®cant, but in the treatments having
fertiliser manure combination, positive and signi®cant trends in yield of rice were observed. Linear regressions ®tted to
pooled data across the locations revealed highly signi®cant
p < 0:01 annual increase in yield of rice with integrated supply
of nutrients through fertilisers and manures, indicating thereby the advantage of combined use of manures plus fertilisers over
fertilisers alone in sustaining crop yields. Soil OC decreased over time at locations where the OC content was greater than
6.5 g kg
ÿ1 at the start of the long-term experiment, but increased at locations having initially low (